rjtedge

Hi all,

I am currently designing my new touring frame and would like some suggestions. I'll start with what I have so far.

I am using oversize tubing with a 36mm HT for the surly LHT fork (45mm rake, 376mm axle to crown) I'm planning to use.
Wheels: 26inch
Seat Tube: 580mm
Top Tube: 573mm
Seat Tube Angle: 73
Head Tube Angle: 73 - I would go 71-72 if I could find suitable head lugs
Chain Stays: 440mm
Cranks: 170mm

So my questions are
1. Bottom Bracket drop/height: I was going to go with a 75mm drop, but I was looking at the LHT and they have such a small drop, only 47mm. Could anyone suggest why the drop is so small? I would think a touring frame would not have to worry about pedal strike.

2. Should I go with oversize tubing? I am a very light (55kg) rider, but will be loading the bike with about 15kg - 20kg at times.

3. Drop Outs: I was contemplating using articulated angle dropouts to make fitting a little easier.

4. How is the bottom braket angels measured. I understand the ST-DT, ST-CS, but the CS-CS angle is confusing me.What does 7degrees actually mean?

Thanks all!!

mudboy

A drop for a 700c wheeled bike of 75mm would be on the low side of normal. With 26" wheels, since the wheel radius is so much smaller, 45-55mm of drop is going to be the norm. Use a 75mm drop on a 559 wheel and you'll be dragging pedals left and right.

As far as OS tubing, with your weight, I would guess that either a lighter gage OS tube or a 9/6/9 standard diameter tube would be fine. I'd go with OS, though.

Use socketed dropouts. I'm assuming this is your first frame, if this is the case, keep things simple. Trust me on this.

Download and run RattleCAD to design your frame. It will show the angles as you're designing your frame. However, 7* is going to be the angle of the chainstays exiting the BB sockets. I would make sure you're using round or R-O-R chainstays for a touring frame, unless lots of tire clearance is needed (i.e. for knobbies).

rjtedge

Thanks mudboy,

Yep first frame, been doing lots and lots of planning and reading - seems more i read the more questions that arise (a good thing as far as I am concerned).

Do you have any suggestions for a particular chainstay, seems hard to find ones longer than 425mm? What Bottom bracket would work for these?

So out of interest, what is a good bottom bracket height? or good clearance height for cranks?

I also do not have my LHT fork yet and was wondering about the measurements for rattlecad. Surly says that it is 376mm axle to crown. Do this mean a straight line from axle to the crown race? Or a straight line from axle to where the fork blade hits the bottom of the crown? Or the length of the fork blade?

Thanks again

mudboy

Remember that the length of the actual chanistay is just part of the total chainstay length...it's C-C, so once you factor in the BB shell and the dropout, your mitered 425mm stay might yield you a 440mm actual stay length.

I'm designing a 26" wheeled commuter for my wife right now, and I think the BB drop is 55mm. She'll be running 170mm cranks with quill pedals, but isn't the "pedal through corners" type, otherwise I'd probably bump BB drop to 48-50mm.

No idea on the Surly stuff, I build my own forks.

tuz

Yeah 47 mm of drop is fine for 26" wheels, it's equivalent to about 77 mm when using 700c wheels. That about as low as it gets.

From the Surly website the axle-to-crown seems to refer to the direct length distance between the race and axle (Usually it is measured along the steerer centreline, not including the rake).

rjtedge

Thanks heaps for the help.

Mudboy - why should I go with Round or R-O-R chainstays for a touring frame? I was going to use 24mm oval stays with .9/.6 wall (like these https://www.cycle-frames.com/bicycle-...0.6-X-425.html ). Should I avoid this? And you are right I forgot to factor in the length of the dropouts into my calculations, so 425mm should get me over the line with ease.

fietsbob

I'd suggest ovalizing an oversize top tube , laying the wide aspect horizontal.

to cure the tail wagging the dog syndrome
of my Specialized Expedition, common round tube, there was always
a bit of a wiggle with every pedal stroke.

so i got together with a cargo bike builder, who used 2 3/4x.049" wall tubes for the rear triangle
and the top tubes..
we stretched the design a bit and made a sloping top tube frame out of them
wits 2 700-40 wheels..

no tail wagging with that, BUT it is a rather heavy Bike, Steel Bruce Gordon racks moved off the SBI.
but as a loaded touring bike it worked quite well.

some weight savings by using the tube shape to get some rigidity laterally. seems practical.

could use same tube to form the downtube, rotated vertical axis..

But maybe the OP has only a light sport touring bike in mind, [then nevermind]
my favorite rides were show up at an airport unpack , toss the carton and ride off..
then look for a book sellers shop for a map ,
and decide where to go next day..
ride eat drink sleep repeat.. maybe find some musicians to play with.

tent sleeping bag and clothing for a cool spring thru fall aboard.

mudboy

Round chainstays will have more lateral stiffness to counter the longer chainstay length. You might not notice a diff if you're light, so oval might work for you.

rjtedge

I like a stiffer ride and on further inspection I found a BB shell (for round stays) that has better angles for my design - round stays it is.

I have to admit I am not a huge fan of the overlized main tubes, but I do appreciate the reasoning. I like a nice round tube front triangle.



This is my design, do you see any problems?

mudboy

What does your trail measurement end up being?

rjtedge

Trail is about 60mm. I think this is ok as I want to use it without front loading and don't want it to be too twitchy without front weight.

mudboy

Yeah, that's probably about right, though my 650b path bomber was built with 52mm and normally carries a handlebar bag and the ride is great. The only other thing (to me) is that the chainstays look a bit on the long side, but I usually go with 425-430mm or so.

Pete

rjtedge

The chainstay length has been something I too have been wondering about. I went for nice and long to begin with as it would allow better loading, but i'm wondering if a little shorter - say 430 would stiffen it up a bit while still absorbing road shock?

mudboy

What's the max tire size you're going to run?

rjtedge

Probably 1.75" would be max. If 2" would fit I would be interested - I usually ride 1.5" and never had bigger than that.

mudboy

Hmm. Well I may just retract my "use round chainstays" comment (or find round-oval-round), then, and 440mm might be about right.

rjtedge

What tire size does the round stays allow?